It is well known that oil and gas well production involves the generation of wastewater by-products, including salt water referred to as brine. Typically, the brine is separated at the well site during the production of gas and oil. The disposal of brine wastewaters in an economic and environmentally safe manner has been a major problem for the oil and gas industries. Such wastewaters contain salt, calcium, oil, soap, barium, strontium, magnesium, iron, and other contaminants, some of which are harmful if discharged untreated into the environment. State agencies require that oil and gas producers, or their service contractors, dispose of their wastewater by approved processes. Storage tanks are erected at the well site to store brine produced from the well. Environmental requirements, imposed by the Environmental Protection Agency and state and local government agencies, require the responsible party associated with the production operations to separate and properly store, transport, and dispose of their wastewater by-products.
Depending upon applicable environmental requirements, the responsible parties associated with the oil and gas production have limited options for the disposal of brine. In most gas and oil producing regions, the brine is filtered and/or chemically treated and then injected into underground disposal wells. For most operations in the Appalachian Basin, the treatment of the brine occurs at a centralized treatment facility. Those facilities typically have higher disposal fees than injection wells. Oil and gas producers are in need of more options for disposal, especially since the cost of transportation will continue to increase. Producers need disposal options that reduce costs, reduce the need for transportation, and protect the environment.
The market for brine disposal encompasses all oil and gas producing regions, including those in the Appalachian Basin, which includes New York, Pennsylvania, West Virginia, Eastern Ohio, Kentucky, and Tennessee. Injection wells for the disposal of the brine have not been successful in most of the Appalachian Basin because of the low porosity and permeability of the rock, the concerns with contamination of fresh groundwater flow, and the need for pretreatment of the brine prior to injection. Therefore, that vast area must be covered by means of permanent centralized facilities for treating the brine.
One brine treatment plant presently operates in Creekside, Pa. That plant is located in Indiana County, at the edge of one of the largest natural gas producing regions in western Pennsylvania. Approximately 90% of the brine processed by that plant is generated from wells within thirty miles of the plant. The remaining 10% is transported from greater distances, as far away as West Virginia, Ohio, and New York. Although most of the brine originates within the surrounding counties, an average cost of $2.10 per barrel is spent on transporting the brine to that brine treatment plant. As shown in Table 1, the transportation costs per barrel increased over the past fifteen (15) years, while the disposal cost decreased. The cost for transporting brine is expected to continue increasing as the associated expenses (i.e., fuel, labor, and truck maintenance) continue to rise.
The prior and related art discloses various processes and apparatuses that function, but are not ideal, for handling brine. One such less than ideal process evaporates the brine within metal pans by burning wellhead natural gas to generate the energy for evaporation. A problem with that approach is that the crystallized salt settles to the bottom of the pan, insulating the remaining brine from the heat source. A second problem is that the units are prone to fires. Additionally, no pretreatment occurs to separate the harmful heavy metals from the brine. The pretreatment allows for the beneficial use of the solid salt product with a reduced risk of those metals entering the surface or groundwater.
Some existing evaporators include a forced circulation falling film evaporator and a rotary drum dryer. The forced circulation falling film evaporator utilizes a two-step approach by which the brine is concentrated within the falling film evaporator and then dried to minimum moisture content inside a secondary device such as a spray-drying chamber. Use of a rotary drum dryer appears to be well suited to some solutions, and could accomplish the evaporation in a single step.
Any solution to evaporating the treated brine is strongly effected by the liquid's characteristics. Properties such as solids concentration, temperature sensitivity of the salts, liquid forming, scaling, and corrosiveness (i.e., to required materials of construction) must be considered. Since brine is usually high in sulfates or calcium carbonate, scale forms on the heat transfer surfaces during evaporation. Also, the brine becomes more corrosive the further concentrated it becomes, which is a problem for some evaporators. A falling film design with heat transfer surfaces arranged in a vertical configuration, allows for high brine concentrations while maintaining high heat transfer rates, minimizing the build up of scale on the heat transfer surfaces.
It is often difficult to locate a supplier of direct-fired falling film evaporators that can operate solely on the available supply of natural gas for energy. The use of steam in combination with mechanical vapor recompression is a common process of supplying the energy for evaporation in this type of evaporator. That approach, while being efficient, requires additional equipment and a supply of treated water to generate the required steam. Also, the required second stage drying chamber must be sufficiently large to prevent the droplets from striking solid surfaces before drying takes place, resulting in large drying chambers. Drying chambers with diameters of eight (8) to thirty (30) feet are common. As a result, this type of evaporating equipment is too costly and too large for providing portable on-site evaporation of the brine.
Many existing water and brine purification techniques utilize reverse osmosis. Examples of such techniques are U.S. Pat. Nos. 4,105,556, 4,188,291, and 4,366,063. The reverse osmosis process tends to be expensive and has limited tolerance to many salts present in brine, particularly calcium salts.
Similarly, U.S. Pat. No. 5,695,643 (“'643 Patent”) teaches a process of treating and disposing of wastewater from oil and gas wells using reverse osmosis. Again, the reverse osmosis procedure is more expensive to employ. Additionally, the process of the '643 Patent utilizes limited pretreatment of the brine and requires that the end product be injected into subterranean formations.
Other alternative processes include: crystallizing the salts (U.S. Pat. Nos. 4,245,998 and 4,797,981), and injecting the water solution into an incinerator in which the salts fuse, the water evaporates, and the organic components burn off (U.S. Pat. No. 4,351,252). Unfortunately, these processes do not employ the pretreatment step of the present invention.
U.S. Pat. No. 4,649,655 (“'655 Patent”) teaches an apparatus for dehydrating slurries; particularly water-based drilling fluids contain drill cuttings. The slurry is injected against a wall of a rotating drum. Flash evaporation of the slurry liquids leaves only the solids on the drum, which can be scraped off. This invention is not designed to be mobile, nor is it designed to be connected to an on-site brine tank. It cannot handle concentrated brine and does not include the necessary pretreatment step, which is essential to any apparatus' ability to positively impact the environment. The lack of a pretreatment step also affects the quality of the solid remaining after dehydration of the slurry. In the present invention, the pretreatment removes the metals from the brine, leaving a purer, salable salt product of the brine evaporation. The '655 Patent lacks an ability to produce such a product. Additionally, the invention disclosed by the '655 Patent is labor intensive in comparison to the unmanned operation of the evaporator unit of the present invention.
U.S. Pat. No. 4,804,477 (“'477 Patent”) teaches an apparatus and process for concentrating oil well brine at the well site. The '477 Patent suffers from the same shortcoming of not using pretreated brine, which would remove the metals before the brine evaporates. The apparatus and process have other shortcomings as well. Two men must attend to the apparatus while it runs. Additionally, the invention disclosed by the '477 Patent uses a condensate collection system, whereas the present invention discharges the vapors into the atmosphere. The invention of the '477 Patent uses internal evaporation, as opposed to the hot surface, rotating drum of the present invention. Finally, the present invention involves direct heating, whereas the '477 Patent uses an internal boiler with a shell.
The present invention utilizes another process of brine evaporation, which consists of a heated metal cylinder on the outside of which is a thin layer of brine that evaporates to dryness. The dried salt is scraped off the cylinder as it revolves. This approach offers an advantage because a rotary drum can be heated directly by a natural gas-fired burner, which allows the evaporator to be utilized at the well site. That single step process also reduces the amount of equipment required for placement on the skid, which alleviates some concerns about space. Space is otherwise a great concern because a natural gas powered generator is required to supply the electricity necessary for the brine pump, motors, and system controls.
The present invention, therefore, provides a novel on-site brine treatment unit, method, and system to safely, efficiently, and effectively evaporate brine. The development of the present invention's portable brine treatment unit, method, and system lower costs to producers with marginal wealth, thus, increasing competition. The cost of on-site treatment will be considerably lower than centralized treatment due to the lower capital costs, fewer man hours, and lower transportation costs. The only requirement for processing of the brine is an available supply of natural gas. It is estimated that through successful on-site treatment, brine could be processed for approximately $1.26 per barrel or $0.03 per gallon, representing a 40% cost savings to Appalachian producers. Also, less time is needed for on-site treatment making it possible that up to four different sites could be processed during a given shift of an employee, depending on the location, volume, and quality of the brine. The novel evaporator unit, method, and system of the present invention, in particular, will greatly change the disposal market by providing the industry greater convenience at a lower cost.
Salt is a salable product of the on-site evaporation of brine. It has been estimated that an average of 1.5 to 1.75 lbs. of salt (sodium chloride and calcium chloride) can be recovered from each gallon of brine that is evaporated. Evidence established that salt produced through the operation of a 30,000 gallon/day/operator/crystalizer at traditional evaporator plants in the early 1990s sold without any difficulties.
Table 2 provides a typical analysis of the salt product and shows that over 95% by weight is comprised of chloride such as calcium chloride, sodium chloride, and magnesium chloride. Several minor constituents exist in much lower concentrations. The salt, although not of sufficient purity for food grade use, could be used for dust suppression, roadbed stabilization, and the control of ice on road surfaces. Hydgroscopic compounds, such as calcium chloride, have proven to be an effective agent to suppress dust and stabilize roadbeds. Commercial products in the form of solid salts have been effectively used for many years in road treatments.
TABLE 2Typical Analysis of Salt Recovered ThroughEvaporation of Treated BrineWeight PercentMajor ConstituentsCaCl220NaCl75MgCl2 2CaSO4 1Minor ConstituentsBaSO4 66 ppmLiCl240 ppmFe 2 ppmHeavy Metals <5 ppm
The success of the brine evaporator unit, method, and system of the present invention is influenced significantly by the use of a pretreatment step. Those skilled in the art will recognize that a variety of different pretreatment processes may be used. One example process is discussed here for purposes of illustration and not limitation. Preferably, a pretreatment process will be chosen that satisfies governmental regulations for disposal. The process should remove contaminants and settleable solids from the brine, such as heavy metals and crude oil.
The chosen pretreatment process should be able to occur at the well site by erecting a storage and/or pretreatment tank at the well site. Brine would be pumped from a storage tank into a pretreatment tank. The brine should be treated and/or filtered to remove all solids and contaminants. Finally, treated brine should be pumped into a temporary tank and will be ready for evaporation.